《Mysql入門MySQL 分表優化試驗代碼》要點：
本文介紹了Mysql入門MySQL 分表優化試驗代碼，希望對您有用。如果有疑問，可以聯系我們。

這里的分表邏輯是根據t_group表的user_name組的個數來分的.
因為這種情況單獨user_name字段上的索引就屬于爛索引.起不了啥名明顯的效果.

1、試驗PROCEDURE.
DELIMITER $$
DROP PROCEDURE `t_girl`.`sp_split_table`$$
CREATE? PROCEDURE `t_girl`.`sp_split_table`()
BEGIN
? declare done int default 0;
? declare v_user_name varchar(20) default '';
? declare v_table_name varchar(64) default '';
? -- Get all users' name.
? declare cur1 cursor for select user_name from t_group group by user_name;
? -- Deal with error or warnings.
? declare continue handler for 1329 set done = 1;
? -- Open cursor.
? open cur1;
? while done <> 1
? do
??? fetch cur1 into v_user_name;
??? if not done then
????? -- Get table name.
????? set v_table_name = concat('t_group_',v_user_name);
????? -- Create new extra table.
????? set @stmt = concat('create table ',v_table_name,' like t_group');
????? prepare s1 from @stmt;
????? execute s1;
????? drop prepare s1;
????? -- Load data into it.
????? set @stmt = concat('insert into ',v_table_name,' select * from t_group where user_name = ''',v_user_name,'''');
????? prepare s1 from @stmt;
????? execute s1;
????? drop prepare s1;
??? end if;
? end while;
? -- Close cursor.
? close cur1;
? -- Free variable from memory.
? set @stmt = NULL;
END$$

DELIMITER ;
2、試驗表.
我們用一個有一千萬條記錄的表來做測試.

mysql> select count(*) from t_group;
+----------+
| count(*) |
+----------+
| 10388608 |
+----------+
1 row in set (0.00 sec)

表結構.
mysql> desc t_group;
+-------------+------------------+------+-----+-------------------+----------------+
| Field?????? | Type???????????? | Null | Key | Default?????????? | Extra????????? |
+-------------+------------------+------+-----+-------------------+----------------+
| id????????? | int(10) unsigned | NO?? | PRI | NULL????????????? | auto_increment |
| money?????? | decimal(10,2)??? | NO?? |???? |?????????????????? |??????????????? |
| user_name?? | varchar(20)????? | NO?? | MUL |?????????????????? |??????????????? |
| create_time | timestamp??????? | NO?? |???? | CURRENT_TIMESTAMP |??????????????? |
+-------------+------------------+------+-----+-------------------+----------------+
4 rows in set (0.00 sec)

索引情況.

mysql> show index from t_group;
+---------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| Table?? | Non_unique | Key_name???????? | Seq_in_index | Column_name | Collation | Cardinality | Sub_part | Packed | Null | Index_type | Comment |
+---------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
| t_group |????????? 0 | PRIMARY????????? |??????????? 1 | id????????? | A???????? |??? 10388608 |???? NULL | NULL?? |????? | BTREE????? |???????? |
| t_group |????????? 1 | idx_user_name??? |??????????? 1 | user_name?? | A???????? |?????????? 8 |???? NULL | NULL?? |????? | BTREE????? |???????? |
| t_group |????????? 1 | idx_combination1 |??????????? 1 | user_name?? | A???????? |?????????? 8 |???? NULL | NULL?? |????? | BTREE????? |???????? |
| t_group |????????? 1 | idx_combination1 |??????????? 2 | money?????? | A???????? |??????? 3776 |???? NULL | NULL?? |????? | BTREE????? |???????? |
+---------+------------+------------------+--------------+-------------+-----------+-------------+----------+--------+------+------------+---------+
4 rows in set (0.00 sec)

PS:
idx_combination1 這個索引是必須的,因為要對user_name來GROUP BY.此時屬于松散索引掃描!當然完了后你可以干掉她.
idx_user_name 這個索引是為了加快單獨執行constant這種類型的查詢.
我們要根據用戶名來分表.

mysql> select user_name from t_group where 1 group by user_name;
+-----------+
| user_name |
+-----------+
| david???? |
| leo?????? |
| livia???? |
| lucy????? |
| sarah???? |
| simon???? |
| sony????? |
| sunny???? |
+-----------+
8 rows in set (0.00 sec)

所以結果表應該是這樣的.
mysql> show tables like 't_group_%';
+------------------------------+
| Tables_in_t_girl (t_group_%) |
+------------------------------+
| t_group_david??????????????? |
| t_group_leo????????????????? |
| t_group_livia??????????????? |
| t_group_lucy???????????????? |
| t_group_sarah??????????????? |
| t_group_simon??????????????? |
| t_group_sony???????????????? |
| t_group_sunny??????????????? |
+------------------------------+
8 rows in set (0.00 sec)

3、對比結果.


mysql> select count(*) from t_group where user_name = 'david';
+----------+
| count(*) |
+----------+
|? 1298576 |
+----------+
1 row in set (1.71 sec)

執行了將近2秒.

mysql> select count(*) from t_group_david;
+----------+
| count(*) |
+----------+
|? 1298576 |
+----------+
1 row in set (0.00 sec)
幾乎是瞬間的.

mysql> select count(*) from t_group where user_name <> 'david';
+----------+
| count(*) |
+----------+
|? 9090032 |
+----------+
1 row in set (9.26 sec)
執行了將近10秒,可以想象,這個是實際的項目中是不能忍受的.
mysql> select (select count(*) from t_group) - (select count(*) from t_group_david) as total;
+---------+
| total?? |
+---------+
| 9090032 |
+---------+
1 row in set (0.00 sec)
幾乎是瞬間的.


我們來看看聚集函數.
對于原表的操作.

mysql> select min(money),max(money) from t_group where user_name = 'david';
+------------+------------+
| min(money) | max(money) |
+------------+------------+
|????? -6.41 |???? 500.59 |
+------------+------------+
1 row in set (0.00 sec)
最小,最大值都是FULL INDEX SCAN.所以是瞬間的.
mysql> select sum(money),avg(money) from t_group where user_name = 'david';
+--------------+------------+
| sum(money)?? | avg(money) |
+--------------+------------+
| 319992383.84 | 246.417910 |
+--------------+------------+
1 row in set (2.15 sec)
其他聚集函數的結果就不是FULL INDEX SCAN了.耗時2.15秒.

對于小表的操作.
mysql> select min(money),max(money) from t_group_david;
+------------+------------+
| min(money) | max(money) |
+------------+------------+
|????? -6.41 |???? 500.59 |
+------------+------------+
1 row in set (1.50 sec)
最大最小值完全是FULL TABLE SCAN,耗時1.50秒,不劃算.以此看來.
mysql> select sum(money),avg(money) from t_group_david;
+--------------+------------+
| sum(money)?? | avg(money) |
+--------------+------------+
| 319992383.84 | 246.417910 |
+--------------+------------+
1 row in set (1.68 sec)

取得這兩個結果也是花了快2秒,快了一點.

我們來看看這個小表的結構.
mysql> desc t_group_david;
+-------------+------------------+------+-----+-------------------+----------------+
| Field?????? | Type???????????? | Null | Key | Default?????????? | Extra????????? |
+-------------+------------------+------+-----+-------------------+----------------+
| id????????? | int(10) unsigned | NO?? | PRI | NULL????????????? | auto_increment |
| money?????? | decimal(10,2)??? | NO?? |???? |?????????????????? |??????????????? |
| user_name?? | varchar(20)????? | NO?? | MUL |?????????????????? |??????????????? |
| create_time | timestamp??????? | NO?? |???? | CURRENT_TIMESTAMP |??????????????? |
+-------------+------------------+------+-----+-------------------+----------------+
4 rows in set (0.00 sec)

明顯的user_name屬性是多余的.那么就干掉它.
mysql> alter table t_group_david drop user_name;
Query OK, 1298576 rows affected (7.58 sec)
Records: 1298576? Duplicates: 0? Warnings: 0

現在來重新對小表運行查詢

mysql> select min(money),max(money) from t_group_david;
+------------+------------+
| min(money) | max(money) |
+------------+------------+
|????? -6.41 |???? 500.59 |
+------------+------------+
1 row in set (0.00 sec)

此時是瞬間的.
mysql> select sum(money),avg(money) from t_group_david;
+--------------+------------+
| sum(money)?? | avg(money) |
+--------------+------------+
| 319992383.84 | 246.417910 |
+--------------+------------+
1 row in set (0.94 sec)

這次算是控制在一秒以內了.

mysql> Aborted

小總結一下：分出的小表的屬性盡量越少越好.大膽的去干吧.

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